This invention is directed to fluoride ion as a cure promoting catalyst for compositions containing silicon-containing resins. The compositions can be utilized as coating compositions as well as for other purposes. More particularly, this invention is directed to a composition containing a silicon-containing resin and fluoride ion as a cure promoting catalyst which composition can be cured at low temperature, preferably ambient temperature, to a film having an excellent combination of appearance and durability properties.
The coatings industry has been extensively involved in energy conservation activity for a number of years. Most coating compositions require an elevated temperature of at least about 120 degrees Celsius (.degree.C.) for curing purposes. This represents a considerable expenditure of energy. Additionally, coating compositions which are intended for use in the automotive refinish area often times are applied under conditions such that the aforementioned elevated temperatures are not available for curing purposes. Ideally, the coating composition which can be cured at relatively low temperatures, for example, below about 82 degrees Celsius, and preferably at ambient temperature, would be most useful. Previous attempts to develop such coating compositions have resulted in compositions which were disadvantageously slow to cure and/or produced films which were deficient in one physical property or another.
Coating compositions containing various silicon-containing, film forming resins have been under study as possible alternatives to generally known coatings utilized in applications such as those requiring the coatings to cure to films having a combination of high performance properties. One reason for the interest in these resins is that silicon-containing film forming resins offer the possibility of developing coatings which can utilize atmospheric moisture for curing. Another is that they offer the possibility of an alternative curing mechanism to generally known curing mechanisms such as those which depend on isocyanates to achieve curing. However, there have been a number of problems associated with the utilization of silicon-containing resins which militate against the use of such film forming resins, especially in the high performance coatings area. Just one of the problems with the utilization of silicon-containing film forming resins in coatings applications has been the relatively long period of time that such resins can require to develop reasonably acceptable durability properties. This has been a serious drawback, for example, to the utilization of various silicon-containing film forming resins as moisture curable resins in high performance coatings applications as found, for example, in both automobile original equipment manufacture and in automobile refinishing.
Additionally, in a coating method known as "color plus clear" which is becoming increasingly popular, particularly in the automotive industry, the choice of film forming resins for such a coating system is often limited by the curing properties of the resin such as cure rate as well as final appearance and durability properties of the cured composite coatings produced utilizing this method. It would be desirable to provide a more useful range of film forming resins which could be advantageously utilized in the color plus clear method. Likewise, it would be desirable to provide improved curing rates for the coating compositions utilized in the color plus clear method.
In the color plus clear method (or color plus clear system), a substrate is coated with one or more applications of a pigmented basecoating composition to form a basecoat which thereafter is coated with one or more applications of an essentially clear topcoating composition to form a topcoat. There are several additional disadvantages with known color plus clear systems. After conventional basecoating compositions are applied to the substrate, a rather long period of time, on the order of about 30 minutes or more, may be required between the application of the conventional basecoating composition and the conventional topcoating composition. Such a period is needed to prevent adverse attack by components of the conventional topcoating composition, particularly solvents, on the basecoating composition at the interface of the two, a phenomenon often referred to as strike-in. Strike-in adversely affects the final appearance properties of the coated product. Strike-in is an especially serious problem when metallic flake pigments are employed in the basecoating composition. Strike-in, among other things, can destroy the desired metallic flake orientation in the basecoat.
The present invention is directed to alleviating these and other problems associated with the use of silicon-containing film forming resins, particularly in coatings applications, and more particularly in the area of high performance coatings applications.